Why do some forks and frames have brake rotor size limits?

Jeff Liebermann writes:

On Tue, 24 Oct 2017 23:11:15 -0400, Frank Krygowski
wrote:

On 10/24/2017 8:13 PM, Jeff Liebermann wrote:
On Sun, 22 Oct 2017 09:06:07 -0700, Jeff Liebermann
wrote:

Have you considered adding a water mist brake cooling system instead?

Curses, it's not going to work. The problem is that a very fine water
mist sprayed at a red hot brake disk will vaporize (evaporate) the
tiny water droplets before they hit the red hot brake disk. That's
nice for evaporative cooling the air around the brakes, but does
nothing to cool the actual brake disk. To do that would require
larger droplets, a higher velocity droplet spray, or both. Dumping
liquid water on the brakes would also work, but that's like having
your own private rain storm, which was the original problem.

Grumble...

No problem. You pump it into the right end of a hollow axle, and provide
channels connecting that with the inner hollows in a double-sided disc
similar to an automotive disc, like this:
http://www.autopartsapi.com/eEuropar...169e817e2b.jpg

The water flows out radially, carrying heat with it but leaving the
braking surface dry.

Yep, that will work if we can figure out a way to get the water out of
the hollow axle, through a series of holes drilled into the axle,
without weakening the axle. Cooling channels would make the brake
disk rather thicker. Never mind spraying the bicycle and rider with
scalding hot water or steam while braking. Fenders for disk brakes?

I was hoping that it could be done without any major modifications to
the existing disk brake system. It might be possible to modify the
brake shoes to inject some cooling water. That would go directly onto
the hot brake disk, which is exactly where it's needed most. The
water would cause some slippage, but would evaporate instantly when
red hot. For lower temperatures, the water would simply be turned off
and not used. This might cause some "interesting" braking effects at
the transition point, but I think that can be managed with practice.

Surely the first step is just internal air passages in the brake disks,
as used in motor vehicles for years and years. Any other coolant is a
big step up in difficulty. Unfortunately that would be a major
modification.

On Thursday, October 26, 2017 at 10:22:12 AM UTC-7, Frank Krygowski wrote:
On 10/25/2017 10:53 AM, Joerg wrote:
When it rains
heavily and I have to do a surprise emergency stop after not having used
the brakes for a while there is 1-2sec of nada, absolutely nothing. It
makes no difference whatsoever whether I use $17 high-falutin Koolstop
rain-rated pads or $4 Clarks pads. The experience of other riders around
here and in this NG is similar.

My experience: Koolstops are definitely better than cheaper pads.

Yes, in heavy rain, there's a bit of delay. It's never mattered to me,
probably because I don't seem to require surprise emergency stops. I'm
big on paying attention and anticipating problems. I always have been.

These post-retirement days, I don't do much riding in the rain. (Well, I
did yesterday, but that was unusual.) But I can't see ever buying a disc
brake bike.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

And ISTM that this is yet another example of "safety inflation." For
decades and decades, cyclists rode in all weather using caliper brakes.
They removed their hands from the brake levers to shift gears. They rode
at night using halogen or even vacuum headlight bulbs powered by
dynamos, and in daylight with no lights at all. They had shoes without
custom attachments to the pedals. They wore cloth caps, or no caps at
all. They rode wearing clothing with natural, non-blinding colors.

Now every one of those practices is portrayed by some as scandalously
risky. Sheesh!

Considering the kind of riding that Joerg does surprise emergency stops are the order of the day don't you think? If he can get large sidewall cuts in tires the rest of us have never heard of certainly he riding a hell of a lot harder than the rest of us.

On Thursday, October 26, 2017 at 10:37:02 AM UTC-7, Radey Shouman wrote:
Joerg writes:

On 2017-10-24 17:21, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

[ ... ]

The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.


It seems Californian rain and Thai rain aren't the same. When it rains
heavily and I have to do a surprise emergency stop after not having
used the brakes for a while there is 1-2sec of nada, absolutely
nothing. It makes no difference whatsoever whether I use $17
high-falutin Koolstop rain-rated pads or $4 Clarks pads. The
experience of other riders around here and in this NG is similar.

I don't understand the difference myself. When it's really raining,
meaning there's a continuous film of water on the road and a rooster
tail shooting forward off the front tire, I ride like a little old lady,
because of the delay in braking. Especially when it's dark, and leaves
and other blown down crap cover the road.

I am with you that a super strong brake hardly seems the thing you want in rain.

On Wednesday, October 25, 2017 at 8:59:47 AM UTC-7, wrote:
On Tuesday, October 24, 2017 at 5:22:03 PM UTC-7, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

On 2017-10-24 07:27, wrote:
On Tuesday, October 24, 2017 at 2:19:48 AM UTC-7, John B. wrote:
On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 12:48:29 +0700, John B.
wrote:

On Sun, 22 Oct 2017 20:51:15 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 07:02:08 +0700, John B.
wrote:

But re disc brake cooling F1 car brakes appear to work with
the discs red hot. In the 1,000 degree (F) range. And they
use Carbon Fiber discs too :-) And everyone knows that CF
is better.

"Thermal Conductivity of Carbon Fiber, and other Carbon
Based Materials"
http://www.christinedemerchant.com/carbon_characteristics_heat_conductivity.html


"So...Is Carbon Fiber a good heat conductor?
As usual the answer is "it depends." The short answer is NO
not when regular carbon fiber is made up in regular epoxy and
expected to conduct heat across the thickness. IF a highly
carbonized pan fiber with graphite or diamond added, is
measured for heat transmission in the length of the fiber it
is very good and can rival and exceed copper."

On the other hand, they seem to work pretty well :-) See
https://www.youtube.com/watch?v=h5JcHAEmIYM for a visual
indication of heat dissipation. :-)

Impressive. I'll assume it's a carbon-carbon rotor, since all F1
cars seem to using them.

Undoubtedly so. But if the advantage of "carbon" bikes can be
extolled that a carbon-carbon frame must have twice the bragging
rights :-)


http://www.racecar-engineering.com/technology-explained/f1-2014-explained-brake-systems/


(4 pages)
"A typical road car uses a cast iron brake disc with an organic
brake pad. In an F1 car, though, the same material is used for
both disc and pad, and this material is known as carbon-carbon -
a significantly different material to the carbon-fibre
composites used in the rest of the car" In other words, the F1
brakes are NOT made from CF.

Some detail on Formula 1 brakes:
https://www.youtube.com/watch?v=ev6XTdlKElw

Fun destroying brakes:
https://www.youtube.com/watch?v=KslGsXMgmqg The brake starting
at 4:45 sure looks like CF but I'm not sure.

Maybe twin disk brakes would be easier?
http://nuovafaor.it//public/prodotto/75/nccrop/DOPPIO_FRENO_CROSS_ENDURO.jpg


https://i.ytimg.com/vi/Pvwj-WWlKkg/maxresdefault.jpg
https://gzmyu4ma9b-flywheel.netdna-ssl.com/wp-content/uploads/2011/09/Gatorbrake-dual-hydraulic-front-disc-brakes-carbon-rotors01.jpg


https://lh4.googleusercontent.com/-cDfAFWrGR6Q/VHKPsm-f6YI/AAAAAAAAX10/2FCyj87xs0g/s640/14%2520-%25201.jpg
https://www.minibikecraze.co.uk/wp-content/uploads/bs0978.jpg
https://endless-sphere.com/forums/viewtopic.php?f=28&t=56268

Given the coefficient of friction between a 1.25" wide rubber tire
(32mm) and a wet road probably dragging the feet will work. :-)

Joerg's experience is with full suspension MTB's. These things are
incredibly heavy and long wheelbased. He has his judgement of disks
and it is no doubt quite accurate for his experience and riding.

I have disks on a much lighter and shorter wheelbased bike. I know
the failings up close and personal. I simply cannot imagine WHY a
person would want a more complicated system than that offered by the
Campy Skeleton brakes.


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.

This is something I just can't understand. Indeed there is a millisecond or two delay for the brake shoe to excise the water directly in front of the initial application of the brake but after the brake shoe touches the rim it pushes any water in the way off without floating the shoe above it.

I see no reason whatsoever for disk brakes and their complications even on most MTB's since a good V-Brake is longer lasting, just as effective, cheaper and doesn't require special wheels and frame and fork changes.

If you ride a lot in the rain and use a rim brake, you might go through a front rim every 1-2 years -- at least based on the experience of one of my commuter cohorts who just switched to discs.

My cable discs are pretty simple and stop well -- better than rim brakes in rain. My hydraulic discs are even stronger, but it is true that it is easy to lock the rear wheel. Front braking is not a lot different than a rim brake, IMO. It's the power of the rear brake that takes some adjustment. They can also scream when wet.

I was riding with a friend last week. Both of us were on discs, and his squealed in augmented fourths and then alternated like a European siren. It was annoying and funny at the same time.

-- Jay Beattie.

jbeattie writes:

On Wednesday, October 25, 2017 at 8:59:47 AM UTC-7, wrote:
On Tuesday, October 24, 2017 at 5:22:03 PM UTC-7, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:


[ ... ]


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.

This is something I just can't understand. Indeed there is a
millisecond or two delay for the brake shoe to excise the water
directly in front of the initial application of the brake but after
the brake shoe touches the rim it pushes any water in the way off
without floating the shoe above it.

I see no reason whatsoever for disk brakes and their complications
even on most MTB's since a good V-Brake is longer lasting, just as
effective, cheaper and doesn't require special wheels and frame and
fork changes.

If you ride a lot in the rain and use a rim brake, you might go
through a front rim every 1-2 years -- at least based on the
experience of one of my commuter cohorts who just switched to discs.

And the slowly dying rims generate some really messy black sludge, at
least in my experience. I'm not sure why the "wax your chain to stay
clean" cohort hasn't noticed.


My cable discs are pretty simple and stop well -- better than rim
brakes in rain. My hydraulic discs are even stronger, but it is true
that it is easy to lock the rear wheel. Front braking is not a lot
different than a rim brake, IMO. It's the power of the rear brake
that takes some adjustment. They can also scream when wet.

I was riding with a friend last week. Both of us were on discs, and
his squealed in augmented fourths and then alternated like a European
siren. It was annoying and funny at the same time.

-- Jay Beattie.

--

On 10/26/2017 4:48 PM, jbeattie wrote:

I was riding with a friend last week. Both of us were on discs, and his squealed in augmented fourths and then alternated like a European siren. It was annoying and funny at the same time.

That happened to me about two years ago. It was a club ride in honor of
a prominent club member who had recently passed away. I had helped his
widow choose the route of the ride, and it was kind of a big deal.

I was on my touring bike with cantilever brakes. The brakes were fine up
to the previous day, but for some reason they began howling
embarrassingly every time I stopped along this ride. And we stopped
often, at all the sites in our area that had been important to our
friend. I don't remember the musical interval, but I definitely remember
sounding like a British police siren.

We eventually stopped in the cemetery, and while others paid their
respects at his grave, I was busy adding some toe-in to my brakes. But
he would have understood.

--
- Frank Krygowski

On 10/26/2017 5:08 PM, Radey Shouman wrote:
jbeattie writes:

On Wednesday, October 25, 2017 at 8:59:47 AM UTC-7, wrote:
On Tuesday, October 24, 2017 at 5:22:03 PM UTC-7, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:


[ ... ]


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.

This is something I just can't understand. Indeed there is a
millisecond or two delay for the brake shoe to excise the water
directly in front of the initial application of the brake but after
the brake shoe touches the rim it pushes any water in the way off
without floating the shoe above it.

I see no reason whatsoever for disk brakes and their complications
even on most MTB's since a good V-Brake is longer lasting, just as
effective, cheaper and doesn't require special wheels and frame and
fork changes.

If you ride a lot in the rain and use a rim brake, you might go
through a front rim every 1-2 years -- at least based on the
experience of one of my commuter cohorts who just switched to discs.

And the slowly dying rims generate some really messy black sludge, at
least in my experience. I'm not sure why the "wax your chain to stay
clean" cohort hasn't noticed.

Oh, I've noticed! Somehow, I've never mustered the motivation to wax my
rims to prevent it. ;-)


--
- Frank Krygowski

On 2017-10-26 10:43, wrote:
On Thursday, October 26, 2017 at 10:37:02 AM UTC-7, Radey Shouman wrote:
Joerg writes:

On 2017-10-24 17:21, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

[ ... ]

The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.


It seems Californian rain and Thai rain aren't the same. When it rains
heavily and I have to do a surprise emergency stop after not having
used the brakes for a while there is 1-2sec of nada, absolutely
nothing. It makes no difference whatsoever whether I use $17
high-falutin Koolstop rain-rated pads or $4 Clarks pads. The
experience of other riders around here and in this NG is similar.

I don't understand the difference myself. When it's really raining,
meaning there's a continuous film of water on the road and a rooster
tail shooting forward off the front tire, I ride like a little old lady,
because of the delay in braking. Especially when it's dark, and leaves
and other blown down crap cover the road.


Sometimes one has to reach a destination on schedule and slowing down to
little old lady speed isn't always in the cards. That's why I prefer my
MTB on rainy days. It is slightly slower than the road bike but the
brakes are unfazed by rain. They are noisy in the rain though.


I am with you that a super strong brake hardly seems the thing you want in rain.


Not strong but I want a brake that comes on the instant I want it to,
not 1-2sec later. I also found that I can reach in much harder on my MTB
with the knobby tires in rain than I can with he slicks on the road
bike. Just not when there is a road biker right behind me ...

--
Regards, Joerg

http://www.analogconsultants.com/

On Thu, 26 Oct 2017 17:08:10 -0400, Radey Shouman
wrote:

jbeattie writes:

On Wednesday, October 25, 2017 at 8:59:47 AM UTC-7, wrote:
On Tuesday, October 24, 2017 at 5:22:03 PM UTC-7, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:


[ ... ]


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.

This is something I just can't understand. Indeed there is a
millisecond or two delay for the brake shoe to excise the water
directly in front of the initial application of the brake but after
the brake shoe touches the rim it pushes any water in the way off
without floating the shoe above it.

I see no reason whatsoever for disk brakes and their complications
even on most MTB's since a good V-Brake is longer lasting, just as
effective, cheaper and doesn't require special wheels and frame and
fork changes.

If you ride a lot in the rain and use a rim brake, you might go
through a front rim every 1-2 years -- at least based on the
experience of one of my commuter cohorts who just switched to discs.

And the slowly dying rims generate some really messy black sludge, at
least in my experience. I'm not sure why the "wax your chain to stay
clean" cohort hasn't noticed.

It is probably heresy to mention it, but some people wash their bikes,
particularly after riding in the rain. Amazing how easily all that
black sludge washes off with soap and water :-)

--
Cheers,

John B.

On Thu, 26 Oct 2017 13:22:07 -0400, Frank Krygowski
wrote:

And ISTM that this is yet another example of "safety inflation." For
decades and decades, cyclists rode in all weather using caliper
brakes. They removed their hands from the brake levers to shift gears.
They rode at night using halogen or even vacuum headlight bulbs
powered by dynamos, and in daylight with no lights at all. They had
shoes without custom attachments to the pedals. They wore cloth caps,
or no caps at all. They rode wearing clothing with natural,
non-blinding colors.

Now every one of those practices is portrayed by some as scandalously
risky. Sheesh!

Careful, Frank! Someone will confuse you with a conservative.

Although these days even the "new conservatives" are no longer
conservative. They're just mad that their lives suck, looking for some
payback and usually blaming the wrong people. Principled actual
conservatives are sadly becoming rara aves.